In recent years, as a battery expected to be miniaturized, weight-reduced and capacity-increased, a non-aqueous electrolyte-based secondary battery, such as a lithium ion battery, has been suggested and provided for practical uses.
The lithium ion battery includes a positive electrode and a negative electrode, which are capable of reversibly extracting and inserting lithium ions, and a non-aqueous electrolyte.
As a negative electrode material of a lithium ion battery, a Li-containing metal oxide capable of reversibly extracting and inserting lithium ions, such as, in general, a carbon-based material or a lithium titanium oxide (Li4Ti5O12), is used as a negative electrode active material.
On the other hand, as a positive electrode material of a lithium ion battery, a Li-containing metal oxide capable of reversibly extracting and inserting lithium ions, such as lithium iron phosphate (LiFePO4), or an electrode material mixture including a binder or the like, is used as a positive electrode active material. In addition, the positive electrode of a lithium ion battery is formed by coating the electrode material mixture on the surface of a metal foil, called a collector.
Compared with conventional secondary batteries, such as lead batteries, nickel cadmium batteries, nickel hydrogen batteries and the like, lithium ion batteries are used as power supplies for portable electronic devices, such as mobile phones and notebook-type personal computers due to the light weight, small size and high energy thereof. In addition, recently, lithium ion batteries has been studied as high-output power supplies for electric vehicles, hybrid vehicles, electric power tools and the like, and, in order to be used as high-output power supplies for them, the batteries need to have high-speed charging and discharging characteristics. However, an electrode active material, for example, an electrode material including a Li-containing metal oxide capable of reversibly extracting and inserting lithium ions has a problem of low electronic conductivity.
Therefore, as a method to improve the electronic conductivity of an electrode material, it is disclosed that, for example, a plurality of primary particles consisting of an empirical formula of LixAyBzPO4 (herein, A is at least one selected from Cr, Mn, Fe, Co, Ni and Cu; B is at least one selected from Mg, Ca, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y and rare earth elements, and 0≦x<2, 0<y<1.5, 0≦z<1.5) are collected so as to form a secondary particle, and carbon is interposed between the primary particles as an electron conductive material (refer to, for example, Patent Citations 1 and 2).
Patent Citation 1: Japanese Unexamined Patent Application Publication No. 2004-014340
Patent Citation 2: Japanese Unexamined Patent Application Publication No. 2004-014341